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SQL and Temporal Database Research: Unified Review and Future Directions International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 04 Issue: 09 | Sep -2017 www.irjet.net p-ISSN: 2395-0072 SQL and Temporal Database Research: Unified Review and Future Directions Rose-Mary Owusuaa Mensah1, Vincent Amankona2 1Postgraduate Student, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana 2 Postgraduate Student, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana ---------------------------------------------------------------------***--------------------------------------------------------------------- Abstract - Several attempts to incorporate temporal In the early 1990s, a renowned researcher in the database extensions into the Structured Query Language, SQL, one of community, Richard Snodgrass, proposed that temporal the most popular query languages for databases date back extensions to SQL be developed because few of them to the nineteenth and twentieth century. Although a lot of existed. In response to his proposal [1], a committee was work and research has been done on temporal databases formed to consolidate past research and suggestions from and SQL, there exist very limited literature clearly outlining the research community in order to design temporal the various events which have taken place with regards to extensions to the 1992 edition of the SQL standard. Those temporal extensions of SQL over the years till the present extensions, known as TSQL2, were then developed by this state in a concise document. Consequently, researchers need committee and in 1993, they presented proposals to the to gather several pieces of literature before they can obtain ANSI SQL Technical Committee. Based on responses to the a vivid pictorial timeline of the history and the current state proposals, changes were made to the Language, and the of these temporal extensions for research and software definitive version of the TSQL2 Language Specification development purposes. In order to align current research was published as a technical report in September, 1994 with that from the past, there is the need for a consolidation [2]. of information. In this paper, we seek to present the past and current state of temporal support in relational databases Almost five years later, a new standard SQL:1999 [3] was and also describe the various attempts and proposals to to be released and attempts were made to include a introduce temporal extensions into SQL over the years, substandard, SQL/Temporal [4], which comprised parts of discuss their level of success and impact on the most recent the TSQL2 specification. SQL/Temporal failed to make it to SQL standard. We also identify desirable temporal features the SQL:1999 standard because the TSQL2 approach was which have not yet been introduced into any of the SQL heavily criticized. After the unsuccessful attempt, standards and also determine the level of acceptance of the researchers continued to propose features to extend the available SQL temporal extensions by some commercial SQL syntax for temporal support. A decade later, a new database management system vendors. standard SQL:2011[5] has been developed, which provides a substantive support for temporal data management by introducing system-versioned tables, Key Words: SQL, temporal, databases, SQL:2011, DBMS, application-time period tables and bitemporal tables. TSQL2,SQL-92 Although a lot of work and research has been done on 1. INTRODUCTION temporal databases, there exists very limited literature which clearly outlines the various events which have Different users and applications have diverse taken place with regards to temporal extensions of SQL requirements and as such wish to access data at different over the years till the present state in a single document. points in time; this requires a form of database Researchers need to gather several pieces of literature management system which is able to keep track of past, before they can obtain a vivid pictorial timeline of the current and future states of data. Many computer history and the current state of these temporal extensions, applications, such as banking, inventory control, law, for research and software development purposes. It is for medical records and airline reservations deal with time this reason that this paper seeks to provide a state-of-the- varying information: hence it is important that database art survey on the temporal extensions of SQL, identify any management systems, DBMSs, are designed to be able to drawbacks of the current extensions and present further handle the temporal information. A database which research being conducted in this area. The survey provides in-built support for time is referred to as a conducted addresses the questions below: temporal database. Researchers have engaged in the study of temporal concepts in databases over the years and have Which temporal features are available in the written various scientific papers, articles and books in this various SQL standards? area. What are the key activities and research which have been undertaken in the field of temporal © 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 1160 International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 04 Issue: 09 | Sep -2017 www.irjet.net p-ISSN: 2395-0072 databases and their consequent impact on the defined time is used to include temporal information most recent temporal extensions of SQL? which is not handled by transaction time or valid time; and values of user-defined time are not interpreted by a How are the various database vendors adopting DBMS. temporal extensions of SQL to their database management system products? As an example, consider Mr. X who registers for his health insurance on 4th June, 1995. However, the health Are there any shortcomings of the most recent insurance company could not record this information in SQL standard, SQL: 2011 and which further their computer system because of technical challenges. On research is being conducted to solve these 8th July, 1995, the company is able to record Mr. X’s problems? information in their database. In this case, 4th June, 1995 is the valid time start event of his insurance and 8th July, By gathering and analyzing various literature, other 1995 becomes the transaction time. The need for sources of information and extensive research, we attempt temporal support in databases keeps increasing over the to understand the rationale behind the temporal concepts years: From the years 1982 to 1986, about 25 groups in SQL over the years. were also studying time in databases and 60 articles on temporal databases had been released [8]. It therefore 2. TEMPORAL DATABASES became necessary to develop a common consensus glossary on temporal database concepts: this goal was Conventional databases represent the state of information successfully achieved [9]. at a single point in time; new data can be added and modifications to existing data can be easily performed. Many years now, numerous temporal extensions have However, a drawback of these conventional databases been proposed and therefore there is the need to further was the fact that old values were usually lost whenever consolidate information. Unlike temporal databases, changes occurred and as such it was impossible to track conventional databases model the dynamic real world as the change of information over time in the database. Also, a snapshot at a particular point in time, and it may not in the early years, DBMSs provided very limited support reflect the status of the information in the real world. for handling attributes involving time; Application Therefore, as soon as an update is performed on such a programs had to implement functionalities for this database, the old information is lost and answering purpose. Keeping track of data over time was therefore a queries about past states became a major problem. These major problem which needed to be addressed in databases were referred to as snapshot databases [8]. To databases. make such databases up-to-date, DBMSs provide various mechanisms. One of those was to store all the past states Although the relational data model had gained popularity of the snapshot database and index them by the times over the years, it provided very little support for they change (their transaction times). addressing the temporal dimension of data. The need to handle time more comprehensively arose in the early Although this method was a step forward, we could only 1970s especially in the area of medical information keep track of the transaction time history of the database systems, where a patient’s medical history is particularly without any support for history of the real world. Another important [6]. Other application areas which handle time approach to store past information is by using historical related information in databases include banking, databases. These databases record a single historical state inventory management and airline reservation systems. per relation, thereby taking into account the valid time Today, handling data that evolves over time can be [8]. In 1987, when Snodgrass introduced a new temporal effectively done using temporal databases. A temporal relational query language, TQuel [8], he also proposed DBMS therefore has built-in support for time-varying that the approaches to historical and rollback databases data. can be adopted in temporal databases which require support for both valid time and transaction time. In temporal databases, timestamps
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